An official with the U.S. nuclear power regulator has ordered staff to supply documents that could lead to a review of a 2020 approval of a new type of nuclear power reactor after an engineer raised concerns about its ability to withstand earthquakes, documents showed on Wednesday.

Dan Dorman, the executive director for operations at the Nuclear Regulatory Commission (NRC), reviewed a complaint by John Ma, an engineer at the agency, about its approval of the design of NuScale's nuclear power plant.

NuScale, majority owned by construction and engineering company Fluor Corp, which got approval for the design of a 50-megwatt small modular reactor (SMR), is hoping to build the Carbon Free Power Project with multiple reactors at the Idaho National Laboratory, with the first coming online in 2029 and full plant operation in 2030.

Some see SMRs such as NuScale's as a way to cut emissions from fossil fuels and to potentially reduce Europe's dependency on Russian oil and gas. NuScale also wants to build the plants in Poland and Kazakhstan.

In an internal document Ma wrote to NRC officials soon after the 2020 approval, he alleged the design of the building intended to enclose the reactor units and its spent fuel pool did not provide assurance it could withstand the largest earthquake considered without collapsing, and may be vulnerable to smaller earthquakes.

"Collapse of the reactor building ... could potentially cause an early and large release of radioactive materials into the atmosphere and ground, which could kill people," Ma wrote.

In February, Dorman wrote to Ma that he concluded the NRC's basis for accepting NuScale's measure of strength for the reactor's building design "was not sufficiently documented," documents posted on the NRC website on Wednesday showed.

Dorman ordered the agency's Office of Nuclear Reactor Regulation to document its evaluation of NuScale's "stress averaging approach" and, if necessary, to update the application and evaluate whether there are "any impacts" to the 2020 design approval.

It was uncertain whether the additional actions would affect the project's timeline which has been delayed several times.

The NRC press office had no comment beyond what officials said in the documents. Dorman did not immediately respond to a request for comment.

Diane Hughes, vice president, marketing and communications at NuScale, said the NRC's consideration of professional opinions such as Ma's "are an important part of a strong nuclear safety culture."

She said "the robustness of NuScale structures is one aspect that makes the NuScale SMR the safest design ever approved by the NRC."

A science advocacy group said the concerns Ma raised were troubling.

"NuScale's business case is based on its assertion that it is a safer nuclear reactor, now it's time to prove it by addressing these safety concerns," said Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists.